The cured products of epoxy resin compositions each including an epoxy resin and a curing agent are used in various applications including, for example, electronic parts of semiconductor packages and semiconductor chips. For example, Patent Literature 1 discloses a method for producing an epoxy resin having a polyether group in which the number of the repeating units formed of an alkyleneoxy group is less than three. Patent Literature 2 discloses a method for producing an epoxy resin having a polyether group in which the number of the repeating units formed of an alkyleneoxy group is less than six.